Analysis of synergy between beta-lactams and anti-methicillin-resistant Staphylococcus aureus agents from the standpoint of strain characteristics and binding action.

In light of the increasing number of clinical cases resistant to traditional monotherapies and the lack of novel antimicrobial agents, combination therapy is an appealing solution for the treatment of methicillin-resistant Staphylococcus aureus (MRSA) infections. Here, we evaluated the efficacy of anti-MRSA agents, such as vancomycin (VAN), daptomycin (DAP), and linezolid (LZD), in conjunction with 13 beta-lactams and non-beta-lactams. We assessed the in vitro activities of the various combinations against 40 MRSA strains based on the maximum synergistic effect (MSE), an index calculated from the MIC change with a combination agent. Nearly all the anti-MRSA agents, which were combined with beta-lactams as well as VAN and DAP, showed a synergistic effect with arbekacin. VAN also exhibited varying degrees of synergy depending on the type of beta-lactam, whereas DAP and LZD showed similar synergy with different beta-lactams. These effects were confirmed by antibiotic kill curves, except for the apparent interaction between LZD and beta-lactams. The MSE results were analyzed according to strain characteristics including susceptibility to combination agents, staphylococcal cassette chromosome mec type, and presence of the blaZ gene; however, no obvious correlations were observed. In a fluorescence binding assay, the fluorescence intensity of boron-dipyrromethene (BODIPY)-VAN decreased, whereas that of BODIPY-DAP increased in combination with a beta-lactam agent. These findings suggest that beta-lactam combinations are promising treatment options for MRSA infections and that the type of beta-lactam combined with VAN is important for the synergistic effect.

Evaluation of the double-disk synergy test for New Delhi metallo-ß-lactamase-1 and other metallo-ß-lactamase producing gram-negative bacteria by using metal-ethylenediaminetetraacetic acid complexes.

New Delhi metallo-ß-lactamase-1 (NDM-1), one of the metallo-ß-lactamases (MBLs), has been identified from clinical isolates worldwide. Rapid detection of NDM-1 producers is necessary to prevent their dissemination. Seven types of EDTA complexes were evaluated as MBL inhibitors in double-disk synergy tests (DDSTs), resulting in detection of the first isolate of NDM-1-producing Escherichia coli (NDM-1 Dok01) in Japan. NDM-1 Dok01 was detected when EDTA magnesium disodium salt tetrahydrate (Mg-EDTA), EDTA calcium disodium salt dihydrate, EDTA cobalt disodium salt tetrahydrate and EDTA copper disodium salt tetrahydrate were used as MBL inhibitors. The sensitivity and specificity of DDSTs using Mg-EDTA for 75 MBL producers and 25 non-MBL producers were 96.0% and 100%, respectively. These findings indicate that the DDST method using Mg-EDTA can detect MBL-producing strains, including NDM-1 producers.

Development of interpretive criteria for tebipenem disk diffusion susceptibility testing with Staphylococcus spp. and Haemophilus influenzae.

Disk diffusion susceptibility interpretive criteria for tebipenem against Staphylococcus spp. and Haemophilus influenzae were developed using the Clinical and Laboratory Standards Institute (CLSI) guidelines. Tebipenem was tested by disk diffusion and broth microdilution methods against 119 clinical isolates of Staphylococcus spp. and 102 clinical isolates of H. influenzae. The zone diameters of 5-, 10-, and 30-µg disks were compared with broth microdilution minimum inhibitory concentration (MIC) results by scattergram and regression analysis. When the MIC breakpoint of 1 µg/ml was applied to the scattergrams, the 10-µg disk showed good correlation between the zone diameters and the MIC values. The corresponding disk diffusion zone diameter breakpoints with the 10-µg disk for Staphylococcus spp. were ≧22 mm (MIC ≦1 µg/ml) for susceptible, 20-21 mm (MIC = 2 µg/ml) for intermediate, and ≦19 mm (MIC ≧4 µg/ml) for resistant. We also proposed the breakpoint zone diameter of H. influenzae: ≧22 mm (MIC ≦1 µg/ml) for susceptible. These criteria demonstrated that the categorical agreements between disk diffusion and broth microdilution methods for Staphylococcus spp. and H. influenzae were 95.0% and 99.0%, respectively. The discrepancy rates of these criteria were acceptable to the CLSI guidelines.

[Evaluation of Dipstick 'Eiken' Legionella for detection of Legionella pneumophila serogroup 1 urinary antigen using the immunochromatographical method].

Dipstick 'Eiken' Legionella is a reagent for detection of Legionella pneumophila serogroup 1 antigen in urine using the immunochromatographical method. The reagent was evaluated using the reference and clinical isolated strains and clinical specimens. BinaxNOW Legionella and Legionella antigen [Mitsubishi] were evaluated simultaneously. Using four of L. pneumophila serogroup 1 strains, the minimal detectable concentration of Dipstick 'Eiken' Legionella was 5.0 x 10(4) to 2.0 x 10(5) colony forming unit/ml, it was approximate four times high in comparison with other two kits. And no positive reaction was obtained from 45 of non-L. pneumophila serogroup 1 strains. When Dipstick 'Eiken' Legionella was compared with BinaxNOW Legionella among 50 urine samples obtained from patients with pneumonia and 50 urine from healthy adults, the sensitivity was 94.7%, the specificity was 100.0% and the agreement was 99.0%. Dipstick 'Eiken' Legionella is found to be useful diagnostic reagent for Legionella infection in clinical laboratories.